This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Somatic mutations in PIK3CA (phosphatidylinositol-3 kinase, catalytic subunit, alpha isoform) are reported in breast and other human cancers to concentrate at hotspots within its kinase and helical domains. Most of these mutations cause kinase gain of function in vitro and are associated with oncogenicity in vivo. However, little is known about the mechanisms driving tumor development. Recent work has suggested the existence of three distinct mechanisms that produce an oncogenic PIK3CA protein depending on the structural location of the mutated residue. We propose that we can gain insight on the structural impact of oncogenic somatic mutations in PIK3CA and the existence of this multiple mechanism hypothesis by exploring conformational changes that result from these mutations using extensive molecular dynamics simulations. Our simulations will involve the PIK3CA crystal structure that contains both the PIK3CA catalytic and regulatory subunits, solvated in an explicit water solvent box resulting in the total system size of ~305063 atoms.